I don't think there's anything wrong with incest as long as both parties are consenting adults. I think it would be awkward, but I'm not the magical decision maker for everyone. They can do whatever they want, as long as they know what they are agreeing to. I'd say it's not fair for the kids, but it's not fair for kids of ugly parents either, or parents with a lot of down syndrome or something in their genes... If you are an adult and you are informed, you should be able to have sex with any other adult you want, as long as they are also an informed adult.
IF incest was "immoral" (which I don't think it is) I think homosexual incest might be more moral just because they cannot create kids, thus avoiding the social problems that kid might have when other kids learn that his/her parents were already related... However, since kids will also make fun of you for being poor, ugly, fat, short, tall, skinny, black, white, or anything else, I don't think it's fair to decide which kinds of people aren't good enough to reproduce, because then no one would be able to. No one is perfect.